Google has a new Gmail labs add on for emoticon fanatics. When flipped on it adds an additional 1,200 or so to Gmail's emotion selector tool. New categories include things like national flags, more animals, road signs, and animations.
There are 13 categories in all, up from the two that come with the standard Gmail, which means it can take longer to find what you're looking for. All these additional emoticons actually come from Japanese phone carriers, each of which has its own set that works across all handsets. In Gmail's case, your recipient does not need to be a Gmail user to see them since they're simply embedded as image files.